Hundreds of miles of Great Lakes shoreline would be spoiled under a worst-case scenario oil spill in Michigan's Straits of Mackinac, scientists reported Thursday.

The cost of a doomsday spill could be as high as $1.8 billion, including $500 million in cleanup and $678 million in lost tourism revenue in Wisconsin and Michigan, experts said.

A team of scientists from Michigan universities wrote a 400-page draft report on the risks of an extraordinary spill from Enbridge Line 5, a 20-inch twin oil pipeline that runs beneath the Straits of Mackinac, which connects lakes Michigan and Huron at the peak of the Lower Peninsula. A public hearing will be held on Aug. 13 in Harbor Springs.

The impact of a spill would be significant, but the scientists cautioned that their analysis "extends to risks with low probabilities" of occurrence.

Enbridge, a Canadian company, has been under scrutiny since 2010, when one of its pipelines ruptured in southern Michigan, releasing 800,000 gallons of oil into the Kalamazoo River system. Critics say Line 5, which has been transporting oil between Wisconsin and Ontario, Canada, for decades, should be shut down, saying it's old and could be vulnerable to leaks.

No large oil spill has ever occurred in the Great Lakes. Gov. Rick Snyder's administration is expected to determine the pipeline's long-term future by fall, just a few months before he leaves office. One option would be putting the pipeline in a tunnel under the lakebed.

Enbridge insists that Line 5 is safe. The company said a 24-hour control center monitors the pipeline and can shut it down in minutes.

"The scenarios presented in this report are purely hypothetical and the probability of the events actually occurring is extraordinarily unlikely because Enbridge operates our pipelines with multiple layers of safety in mind," spokesman Ryan Duffy said.

The report says a Line 5 rupture could release as much as 58,000 barrels — 2.4 million gallons — of oil and affect hundreds of miles of shoreline in Michigan, Wisconsin and Canada. Cleanup efforts could be affected by the wind, weather and season.

It is "possible that shoreline cleanup operations for a potential spill in the Straits of Mackinac could continue for months to up to two years following the spill," the report states.

A 1953 easement makes Enbridge liable for damage or loss to public or private property, the scientists said.

Line 5 carries light crude oil and natural gas liquids used to make propane. In 2016, more than half of Michigan's propane needs were supplied by the pipeline.

"Line 5 cannot remain in the Straits in its current form," said Keith Creagh, director of the Michigan Department of Natural Resources. "This report highlights the need to continue developing a decommissioning strategy that protects the Great Lakes while at the same time maintaining the critical infrastructure between Michigan's peninsulas that makes us one state."